The working principle of the vacuum plasma cleaning machine is to apply high energy to the gas in a vacuum environment to convert it into a plasma state. The active components that make up the plasma state include ions, electrons, and active groups. These active components "bombard" the surface of the specimen, playing a role in surface cleaning, modification, and other functions.

Obtaining vacuum

In order to achieve a vacuum environment, we need a component that can make the system reach a vacuum environment - a vacuum pump. Depending on the level of vacuum, the corresponding vacuum pump used is also different. For low vacuum environments, mechanical pumps are generally required to maintain it. High vacuum and ultra-high vacuum generally require pump sets of molecular pumps and ion pumps to maintain.

Vacuum pump unit

In principle, vacuum pumps are generally divided into two categories: gas transfer pumps and gas capture pumps. The working principle of the gas transfer pump is to continuously suck the gas inside the chamber into the pump and then discharge it to reduce the pressure inside the chamber. The working principle of a gas capture pump is to adsorb the gas inside the chamber onto the surface inside the pump, without discharging it outside the pump.

Mechanical pumps are classified according to their principles and belong to gas transmission pumps. Mechanical pumps are roughing pumps, located at the forefront, which reduce the system pressure from atmospheric pressure. The principle adopted is to use the expansion, compression, and discharge of gas, and periodically change the volume of the gas chamber to discharge the gas in the container, with the ultimate limit even reaching a vacuum degree of 10-3 torr.

Mechanical pumps are mainly divided into rotary pumps or scroll pumps. These two categories. The physical object and principle of the oil pump are shown in Figure 1-a. The oil pump rotates the rotor inside the pump through the motor outside the pump, and the rotor connected to the rotor continuously opens and closes. The pressure difference caused by this reciprocating motion can continuously remove the gas inside the chamber from the pump. Due to the insufficiently tight design of this working structure, air leakage may occur at the contact part between the rotor and the cavity. To avoid this situation, mechanical pump oil is generally used at the leakage part, which can provide a certain sealing effect. In addition, some oil pumps also use a two-stage pump structure, allowing the front stage pump to exhaust during suction, reducing pressure difference and ensuring pump sealing. However, due to the use of oil for sealing, there are many oil droplets and molecules in the pump body, which can diffuse into the vacuum environment through the inlet and cause pollution, which is also a disadvantage of the oil pump.

Figure 1 Introduction to vacuum pump and its working principle. (a) Physical picture of the oil pump and its working principle diagram. (b) Physical picture and working principle diagram of dry pump.

The dry pump effectively solves the problem of oil pump "reverse oil". The dry pump no longer uses oil film for sealing, but instead uses a tight fit between the dynamic and static rotary discs for sealing. Through clever design, gas enters the gap between the rotating discs from the outermost side, gradually being compressed to the innermost side and discharged through rotation, as shown in Figure 1-b.

Comparison of advantages and disadvantages of dry pump and oil pump

Advantages of oil pump

Fast pumping speed: Oil pumps usually have a high pumping speed, which can quickly pump out the gas in the vacuum system and achieve the required vacuum degree in a short period of time.

High ultimate vacuum degree: In principle, the oil pump has high sealing performance and can achieve better vacuum degree compared to dry pumps.

Disadvantages of oil pump

There is a risk of oil contamination: Oil pumps use oil as the working medium, which may generate oil vapor during operation. These oil vapors may contaminate samples or products in the vacuum system. For some pollution sensitive processes, such as semiconductor chip manufacturing, optical component manufacturing, etc., additional measures need to be taken to prevent oil contamination.

Regular maintenance is required: In order to ensure the performance and lifespan of the oil pump, it is necessary to regularly replace the pump oil, clean the oil filter and oil mist separator, and other components. Maintenance work is relatively frequent and costly.

Not suitable for certain special gases: For gases that are corrosive or undergo chemical reactions with oil, the oil pump may not be able to handle them directly, and a special gas treatment device needs to be added before the inlet, which increases the complexity and cost of the system.

Advantages of dry pump

Clean and pollution-free: The dry pump does not require oil as the working medium during operation, so it will not produce oil vapor pollution and can provide a clean vacuum environment, especially suitable for high environmental requirements such as semiconductor manufacturing, optical industry, etc.

No oil mist emission: As it does not involve the use of oil, the dry pump will not emit oil mist, which is very beneficial for maintaining the cleanliness of the workplace and the health of operators, and also meets environmental protection requirements.

Suitable for multiple processes: able to adapt to various process requirements, including situations with special requirements for vacuum degree and gas processing capability, such as in processes that require the treatment of corrosive gases or gases containing particles, dry pumps can be specially designed to meet the needs.

Low maintenance cost: There is no need to regularly replace pump oil or deal with related issues caused by oil pollution, such as oil filter replacement, oil mist separator maintenance, etc. Therefore, maintenance work is relatively simple and the cost is low.

Disadvantages of dry pumps

Relatively low pumping speed: Compared to oil pumps of the same specifications, dry pumps typically have slower pumping speeds, which means that in applications that require rapid attainment of high vacuum levels, dry pumps may take longer to complete their tasks.

Limited ultimate vacuum degree: Although dry pumps can achieve high vacuum degrees, in general, their ultimate vacuum degrees are not as high as oil pumps. In some experiments or processes that require extremely high vacuum levels, it may not be possible to meet the requirements.

High price: The design and manufacturing technology of dry pumps are relatively complex, so their initial purchase price is usually higher than that of oil pumps, which to some extent increases the investment cost of equipment.

In summary, vacuum plasma cleaning machines with dry pumps and oil pumps each have their own advantages and disadvantages. When choosing, it is necessary to comprehensively consider factors such as specific application requirements, working environment, and budget to determine which pump is more suitable for practical applications.